How many mailboxes can I migrate with a single license?

Answer:

A single license gives you the ability to migrate a single mailbox to a single Destination. A mailbox license may grant you 50GB of data transferred, and up to 10 passes per mailbox.

Here are some examples to help explain how mailbox licenses work:

You cannot migrate ten 5GB mailboxes using a single license.

You cannot use each pass to migrate a different mailbox.

Each pass must be performed against the same mailbox.

When the license limit is reached, the migration will stop. To continue, you must purchase additional licenses. Then you can resubmit the item for migration. The migration will begin where it left off.